Copper Segregation Research Articles

Effect of Selective Milling on the Concentration Process of Critical Raw Materials from MSW Incinerator Bottom Ash

This research introduces selective milling as a reliable and effective initial concentration process to enable efficient separation and ensure high recovery rates of valuable and critical materials (minerals and metals) from processed incinerator bottom ash (pr.IBA), a treated mineral fraction originating from the conventional municipal solid waste (MSW) incinerator bottom ash (IBA) processing steps. Four different types of pr.IBA (each sample weighing up to three tons) were selectively milled using a demonstration-scale vertical roller mill to produce three distinct products: fine, middle, and coarse fractions. Chemical analysis demonstrated that a concentration step after selective milling could be reliably achieved regardless of the variation in the sources and qualities of the input materials. Specifically, calcium-containing compounds can be enriched in the fine fraction, potentially containing Ca2SiO4, CaSO4, and CaCO3. Complementary to its particle size equivalent to the raw mix, this calcium segregation could be valuable as an alternative material in cement clinker production. Conversely, the segregation of metal-bearing substances, particularly iron and copper, was detected in the coarse fraction. Such segregation is comparable to specific ore grades and enhances the possibility of metal recovery from pr.IBA.

Localized corrosion of thermally aged Cu-containing Ni-13Cr-10Fe alloys: The role of Cu enrichment induced grain boundary sensitization

This study reports a new mechanism of grain boundary (GB) sensitization without precipitation of Cr-rich phases at GBs in Cu-containing Ni-Cr-Fe alloys. Copper segregation at GBs during annealing can deplete the boundaries of Cr due to the repulsive interaction between Cr and Cu. The depletion of passivating Cr along GBs can cause intergranular corrosion susceptibility, as evidenced by electrochemical testing and post-mortem morphological characterization. The implications of this new sensitization mechanism on the localized corrosion resistance of Cu-containing commercial alloys are discussed.

Temperature-induced atypical oxidation in Sm2(Co, Fe, Cu, Zr)17 alloy systems: Dependency on oxygen-induced elemental migration

This paper addresses temperature and/or oxygen-induced chemical segregation of elements in the growth of oxide scale on Sm2(Co, Fe, Cu, Zr)17. Whereas, oxidation at T ≤ 573 K leads to primarily iron and cobalt segregation and subsequently their oxides, that at > 573 K, yields to largely CuO because of copper segregation. Only combination of higher sample temperature and environmental oxygen are found to have driven copper from alloy interior to its surface. Moreover, oxidation mechanism is considerably slowed down at higher temperature and is attributed to semi passivating surface copper oxide formation, impeding passage of oxygen to layers underneath to it.

Microstructure, chemical composition, and dielectric response of CaCu3Ti4O12 ceramics doped with F, Al, and Mg ions

Ceramics with nominal chemical composition CaCu3Ti4O12 (CCTO), CaCu3Ti3.96Al0.04O11.96F0.04 (CCTOAF), and Ca0.98Mg0.08Cu2.94Ti3.96Al0.04O11.96F0.04 (CCTOMAF) were prepared by the solid-state reactions technique. Using SEM, EDX, XPS, EPR, NMR, and complex impedance spectroscopy, the microstructure, elements distribution, chemical composition of grains and grain boundaries, and the dielectric response of ceramics were investigated. In the ССТО, CCTOAF, and CCTOMAF series, the average grain size increases, the degree of copper segregation at the grain boundaries is inversely related to grain size, and the dielectric loss decreases from 0.071 to 0.047 and 0.030, respectively, while dielectric permittivity ε′ at 1 kHz is 5.6 × 104, 7.1 × 104, and 4.3 × 104, respectively. Additives of Al, Mg, F and milled particles (ZrO2, Al2O3, and SiO2) can either partially introduce into the perovskite structure or form low-melting eutectics at the grain boundaries, causing abnormal grain growth. The presence of copper ions in various oxidation states, as well as evidence of exchange spin interactions between them, was confirmed in all samples.

Corrosion Resistance of Al0.5CoCrFeNiCuxAgy (x = 0.25, 0.5; y = 0, 0.1) High-Entropy Alloys in 0.5M H2SO4 Solution.

The electrochemical behavior of the as-cast Al0.5CoCrFeNiCuxAgy (x = 0.25, 0.5; y = 0, 0.1) high-entropy alloys (HEAs) in a 0.5M H2SO4 solution was studied. Polarization measurements were carried out in a standard three-electrode electrochemical cell at room temperature using a platinum counter electrode and a saturated silver chloride reference electrode. For Al0.5CoCrFeNiCu0.5 and Al0.5CoCrFeNiCu0.5Ag0.1, copper segregation along the grain boundaries was observed, which highly dissolved in the sulfuric acid solution and resulted in low corrosion resistance of the samples. Introducing Ag into Al0.5CoCrFeNiCu0.25 HEA led to the precipitation of a copper-silver eutectic structure, in which the copper regions were selectively dissolved in the sulfuric acid solution. Al0.5CoCrFeNiCu0.25 exhibited the best corrosion resistance with the corrosion current density of Icorr = 3.52 ± 0.02 μA/cm2, significantly superior to that of the Al0.5CoCrFeNi sample without copper and silver (Icorr = 6.05 ± 0.05 μA/cm2). Finally, the results indicated that suppressing elemental segregation by annealing or tailoring chemical composition is essential to improve the corrosion resistance of Al0.5CoCrFeNiCuxAgy HEAs.

Effect of Copper Segregation at Low-Angle Grain Boundaries on the Mechanisms of Plastic Relaxation in Nanocrystalline Aluminum: An Atomistic Study.

The paper studies the mechanisms of plastic relaxation and mechanical response depending on the concentration of Cu atoms at grain boundaries (GBs) in nanocrystalline aluminum with molecular dynamics simulations. A nonmonotonic dependence of the critical resolved shear stress on the Cu content at GBs is shown. This nonmonotonic dependence is related to the change in plastic relaxation mechanisms at GBs. At a low Cu content, GBs slip as dislocation walls, whereas an increase in Cu content involves a dislocation emission from GBs and grain rotation with GB sliding.

A Lightweight AlCrTiV0.5Cux High-Entropy Alloy with Excellent Corrosion Resistance

Lightweight high-entropy alloys (HEAs) are a new class of low-density, high strength-to-weight ratio metallic structural material. Understanding their corrosion behavior is crucial for designing microstructures for their practical applications. This work investigates the electrochemical corrosion behavior of lightweight HEAs AlCrTiV0.5Cux (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) in a 0.6 M NaCl solution. These HEAs were produced by vacuum arc melting. In contrast to 304L stainless steel, all of the alloys exhibited lower current density levels caused by self-corrosion, with AlCrTiV0.5 demonstrating the highest corrosion resistance (0.131 μA/cm2). Corrosion resistance decreased along with the content of copper because copper segregation accelerated local corrosion throughout the alloy.

Enhanced nanocrystalline stability of BCC iron via copper segregation

Nanocrystalline alloys are known for their high density of grain boundaries (GBs), which results in low thermal stability and a tendency for coarsening. In this work, we investigated Fe–Cu alloys to explore the effects of Cu concentration on the thermal stability of nanocrystalline samples. Using hybrid molecular dynamics (MD) and Monte Carlo (MC) simulations, annealing treatments of nanocrystalline samples with varied Cu concentrations were conducted. The simulation results revealed that Cu atoms tended to accumulate at GBs. Subsequently, the model with Cu segregation was subjected to mechanical creep loading at various temperatures. Through the analysis of atomic structure evolution during creep deformation, it was found that Cu segregation efficiently stabilizes GBs and restricts their movement. The present findings highlight that the thermal stability of nanocrystalline Fe–Cu alloys can be effectively improved by introducing suitable Cu segregation at GBs.

The role of copper crystallization and segregation toward enhanced methanol synthesis via CO2 hydrogenation over CuZrO2 catalysts: A combined experimental and computational study

The role of copper crystallization in the enhanced methanol production via CO2 hydrogenation over CuZrO2 catalysts was explored along with a combination of experimental and computational studies. The catalysts were synthesized by a surfactant-assisted route followed by reflux in a one-pot method. Catalyst structure, bulk properties, surface reactivity, and reaction pathways were evaluated by XRD, BET, FRX, TPR, N2O-TPD, CO2-TPD, in situ DRIFTS, AP-XPS, and XRD. Calculations based on density functional theory (DFT) were performed to explore the formation of possible intermediates in a copper-driven conversion with surface models of the CuZrO2 catalyst. The combination of experiments and DFT results revealed that the intermediate steps of the catalyzed reaction of CO2 hydrogenation into methanol might depend on the incorporation of Cu in the zirconia sample. The catalyst containing only amorphous interfacial sites showed higher performance on CO2-to-methanol hydrogenation compared to the catalysts containing high crystallinity of copper. The superior activity of the 10CuZrO2 catalyst is mainly ascribed to the cooperative effect between the highly dispersed copper nanoparticles and the basic sites.

Effect of bias voltage on the structure and properties of CuNiTiNbCr dual-phase high entropy alloy films

The dual-phase structure has been proved to overcome the effect of strength-ductility trade-off of high-entropy alloys. However, most of the high entropy alloy films with larger atomic size difference tend to form a single amorphous structure under non-equilibrium deposition conditions such as magnetron sputtering. In this study, the dual-phase CuNiTiNbCr high entropy alloy film containing the Cu-rich FCC alloy phase and amorphous phase were synthesized by high-power pulsed magnetron sputtering at different bias voltages. The poor affinity of copper with other elements led to the segregation and enrichment of copper to form a Cu-rich FCC phase. The effects of substrate bias voltage on the microstructure, mechanical and corrosion properties of the films were investigated. With the increase of bias voltage, the content of copper in the film decreased, the stress state of the film changed significantly, and the compactness of the structure was improved. The hardness of all films was higher than that of most other high entropy alloy film systems. The films deposited under low bias voltage have better toughness. The film deposited at －50 V showed the best wear resistance due to a combination of high hardness and good toughness. The film deposited at －150 V showed the best corrosion resistance since it had the lowest self-corrosion current density (6.1 ×10−8 A/cm2), which was due to its compact structure and lower impurity content.

Molecular dynamics simulation and thermodynamics calculation on surface segregation in Ni-Cu nano-films under stress

The surface segregation of Cu atoms in a Ni-Cu system was investigated using molecular dynamics simulations. Thermodynamic calculations were performed to verify the results of the molecular dynamics simulations. For the thermodynamic calculations, a model for evaluating the influence of stress on surface segregation was developed using the modified Darken model in combination with the broken-bond model. Using molecular dynamics simulations, it was found that the enrichment of Cu atoms occurred for a free-standing Ni-10 at.% Cu film consisting of 20 layers. Simultaneously, the stress distribution across the Ni-Cu thin film is obtained. The thermodynamic calculation results show that the influence of stress on the surface segregation cannot be ignored because of the considerable surface stress. Surface tension stress promotes the surface segregation of copper in Cu-Ni alloys due to the larger lattice parameter of copper than nickel, which leads to the reduction of surface strain energy. When the thickness is greater than 31 nm (or the number of layers exceeds 89), the size effect disappears, i.e., the surface concentration doesn’t increase with the increase of thickness. The calculation results obtained by the Bragg-William equation used for the surface segregation in equilibrium are in good agreement with the thermodynamic calculation and molecular dynamics simulation results.

Atom Probe Analysis of Nanoparticles Through Pick and Coat Sample Preparation.

The ability to analyze nanoparticles in the atom probe has often been limited by the complexity of the sample preparation. In this work, we present a method to lift–out single nanoparticles in the scanning electron microscope. First, nanoparticles are dispersed on a lacey carbon grid, then positioned on a sharp substrate tip and coated on all sides with a metallic matrix by physical vapor deposition. Compositional and structural insights are provided for spherical gold nanoparticles and a segregation of silver and copper in silver copper oxide nanorods is shown in 3D atom maps. Using the standard atom probe reconstruction algorithm, data quality is limited by typical standard reconstruction artifacts for heterogeneous specimens (trajectory aberrations) and the choice of suitable coatings for the particles. This approach can be applied to various unsupported free-standing nanoparticles, enables preselection of particles via correlative techniques, and reliably produces well-defined structured samples. The only prerequisite is that the nanoparticles must be large enough to be manipulated, which was done for sizes down to ~50 nm.

Prolonged ordering process induced higher segregation of copper in 2:17 type SmCo magnets

The segregation of Cu is crucial for the magnetic properties of 2:17 type SmCo magnets, which is firstly affected by the ordering process during aging treatment. In this research, the ordering process is successfully regulated by doping nano ZrO2, which achieves a prolonged ordering process and an increased duration of twin boundaries in 2:17 type SmCo magnets. The continuous migration of twin boundaries in a longer period drives extra Cu to converge towards the cell boundary center, resulting in about 10.52 kOe coercivity only by isothermal aging treatment. The precipitation sequence of the lamellar phase and the cell boundary phase is exchanged. A new understanding of Cu segregation contributes to the development of high performance 2:17 type SmCo magnets.

Modification of the Microstructure and Transport Properties of La2CuO4−δ Electrodes via Halogenation Routes

Ruddlesden–Popper type electrodes with composition La2CuO4−δ are alternative cathode materials for solid oxide fuel cells (SOFCs); however, the undoped compound exhibits low electrical conductivity for potential applications, which is usually increased by alkaline-earth doping. A promising alternative to alkaline-earth doping is the modification of the anionic framework by halogen doping. In this study, La2CuO4−0.5xAx (A = F, Cl, Br; x = 0–0.3) compounds are prepared by a freeze-drying precursor method, using an anion doping strategy. The composition, structure, morphology and electrical properties are studied to evaluate their potential use in solid oxide fuel cells (SOFCs). The halogen-doped materials show higher electrical conductivity and improved electrocatalytic activity for oxygen reduction reactions when compared to the pristine material, with polarization resistance values 2.5 times lower, i.e., 0.20, 0.11 and 0.08 Ω cm2 for undoped, F- and Cl-doped samples, respectively, at 800 °C. Moreover, halogen doping prevents superficial copper segregation in La2CuO4−δ, making it an attractive strategy for the development of highly efficient electrodes for SOFCs.

Prolonged Ordering Process Induced Higher Segregation of Copper in 2:17 Type Smco Magnets

Prolonged Ordering Process Induced Higher Segregation of Copper in 2:17 Type Smco Magnets

The nanoscale distribution of copper and its influence on charge collection in CdTe solar cells

For decades, Cu has been the primary dopant in CdTe photovoltaic absorbers. Typically, Cu acceptor concentrations in these devices are on the order of 1 × 1014 cm−3, which has made it notoriously difficult to directly correlate nanoscale Cu distributions to the local charge transport properties of these devices. To measure and correlate these properties, measurement techniques require high sensitivity to elemental concentration, large penetration depth, and operando compatibility. Techniques such as secondary-ion mass spectroscopy and X-ray energy dispersive spectroscopy are widely adopted to measure Cu concentrations, but they are limited by penetration depth, sensitivity, or spatial resolution. Additionally, they lack the operando capabilities required to correlate one-to-one Cu concentrations to electrical performance. In this work, correlative X-ray microscopy is used to investigate the spatial distribution of Cu and its impact on charge collection through the depth and breadth of CdTe photovoltaic devices. Plan-view, nanoscale X-ray fluorescence maps clearly demonstrate the spatial segregation of copper around regions thought to be CdTe grain boundaries. Complementary cross-section imaging unveils the transition of the maximum charge-collection efficiency from the ZnTe–CdTe interface to the CdS–CdTe interface as a function of Cu incorporation. The copper concentration through the depth of the CdTe layer is characterized by slow and fast diffusion components, and cross-section charge-transport modeling shows that the experimentally obtained charge collection can be explained by the modeled acceptor distribution through the depth of the CdTe layer.

The Effect of Tartaric Acid and Citric Acid as a Complexing Agent on Defect Structure and Conductivity of Copper Samarium Co‐Doped Ceria Prepared by a Sol‐Gel Auto‐Combustion Method

Copper samarium co‐doped ceria (CSDC) (Cu0.01Sm0.19Ce0.80O2−δ) nanoparticles were synthesized via a sol‐gel auto‐combustion of metal nitrates without a complexing agent (DI) and with tartaric acid (TA) or citric acid (CA). The solid oxide formation of CSDC/DI corresponds to the endothermic stage, whereas that of CSDC/TA and CSDC/CA matches the exothermic stage caused by the decomposition of the metal cross‐linking and carbon combustion. The cross‐linking occurs more extensively in the CA case as more heat is released in CA than in the TA route. The as‐synthesized morphology of CSDC/DI reveals both layered structures and small agglomerated particles, whereas CSDC/TA and CSDC/CA show dense xerogel and porous xerogel, respectively. The cubic fluorite structure for calcined CSDCs was confirmed by XRD. From Raman analysis, calcined CSDC/CA has the lowest amount of copper segregation and the highest relative total oxygen vacancy concentration []total, whereas calcined CSDC/DI has the highest amount of copper segregation and the lowest []total. For all samples, copper segregation promotes densification, albeit to varying degrees. The relative densities of CSDC/DI, CSDC/TA, and CSDC/CA pellets are 82.8 ± 2.4%, 95.5 ± 1.8%, and 97.8 ± 0.9%, respectively. The sintered CSDC/DI has the lowest density because some copper segregates and liquid copper in interparticle spaces could evaporate earlier than samples containing a complexing agent, whereas sintered CSDC/CA has the highest density because Cu could slowly diffuse from the Cu‐Sm‐Ce solid solution to grain boundary regions and then precipitate as CuO. The specific grain boundary conductivity is predominantly influenced by CuO along grain boundaries, which reduces specific grain boundary conductivity and increases the enthalpy of association (ΔHa) at 250–350°C; however, it rarely impacts total grain boundary conductivity at temperatures higher than 400°C. CSDC/CA has slightly higher total conductivity than CSDC/TA despite having more CuO segregation because it has higher density and .

Numerical modeling of copper macro-segregation in the binary alloy Al-4Cu

In this paper, the modeling of the solidification of Al-4Cu alloy was studied. The calculation code is developed to model the equiaxed globular solidification of the Al-4Cu alloy in a square mold. The mold walls are subjected to constant temperatures and the velocity components are equal to 0, the exchange coefficient ’H’ between the interface of the melt and the mold is estimated at 500 W/( m2 K) and the initial melt temperature ’T0’ is equal to 900 K. The resolution method used is finite differences, the upwind scheme for convective terms, and the space-centered scheme for diffusive terms. The calculated profiles are temperature, solid fraction, concentration and macro-segregation of copper. At the beginning of cooling, the solidification of the Al-4Cu alloy started in the four corners of the plate. The grains formed at the walls could not move in the studied surface. With cooling time, the solidification of the casting developed rapidly in the lower part; because, the grains formed away from the walls sedimented and accumulated in this part of the plate. On other hand, the liquid was located mainly in the upper part. The segregation of copper in the two-phase mixture is due to its continuous rejection from the solid to the liquid.

The effect of small addition of copper on the growth process, structure, surface charge and adsorption properties of ZnO films in the pyrolysis of dithiocarbamates

Highly textured ZnO films are fabricated, the outer polar surface of which is decorated with copper complexes. The segregation of copper on the surface during growth is attributed to the manifestation of the Jahn–Teller effect.

Chemical composition influence on element segregation and properties of steel strip manufactured by strip casting route

The article presents the results of the chemical composition influence on element segregation and properties of steel strip manufactured by strip casting route. It is shown that in the transition from the slab production with a thickness of 220 mm to slabs with a thickness of 1.2 mm, the thickness of the segregated diffusion layer in the case of the continuous strip casting process is 4.1 - 12.4 times less than in the case of traditional continuous casting. The carbon, nitrogen, copper, tin, phosphorus and sulfur segregation percentage in the continuous strip casting process is 1.7 - 5.1 times less than in traditional continuous casting. A method is proposed for calculating the element segregation based on the equality of the segregation level in traditional and strip continuous casting. It has been established that the content of elements in steels during two-roll continuous casting can be increased for impurities such as S, O, N, P, H from a minimum of 3 for P to a maximum of 497% for S. For residual elements such as Pb, Bi, Sn, Cu, Sb, Zn, As minimum increase from 1.1 for Zn to maximum 401% for Pb. The content of such alloying elements as B, Se, Al, Te, Ca, Mg, Ce, C, La, Nb, Ti, Mn, Ni, Si can be increased from a minimum of 1.1 for Si and Mn to a maximum of 675% for B. The time and rate of cooling of a 20-ton coil of steel strip are calculated, which are, respectively, 13.7 hours and 0.0051 oC/s. Such cooling conditions create the prerequisites for the precipitation of chromium carbides and an increase in the tendency of steel to intergranular corrosion. It was found that for eliminate this problem, it is necessary to increase the cooling time with water after rolling to a strip temperature from 300 to 400 oC.